Whisk eggs, milk, smoked paprika, salt, pepper and onion powder together in a large bowl. Pour onto the prepared baking sheet and sprinkle with spinach, Cheddar and ham. Bake until just set, 20 to 25 minutes, rotating the pan from back to front halfway through baking to ensure even cooking. Cut into 12 squares and serve.

To make ahead: Wrap squares individually in plastic wrap or place them in a sealed container between layers of parchment paper; refrigerate for up to 3 days or freeze for up to 3 months. To reheat, remove plastic, wrap in a paper towel and microwave on High for 30 to 60 seconds.